Polyphase oscillator



Dec 1949 e. "r. ROYDEN POLYPHASE OSCILLATOR 2 Sheets-Sheet 1 Filed Sept. 1, 1945 INVENTOR GEORGE ,'T'- WOYDEN ATTORNEY 9 1949 G. T. ROYDEN POLYPHASE oscmmoa 2 Sheets-Sheet 2 Filed Sept. 1, 1945 INVENTOR GEORGE T. ROYDEN ATTORNEY Patented Dec. 27, 1949 POLYPHASE OSCILLATOR George T. Royden, South Orange, N. j"J., assignor to Federal Telephone andiRadioCorporation, "New York, N. Y., a corporation'of Delaware Application: Septembenl, 1945-,cSerialNo. 613 979 9 Claims.

This invention relates to the generation of polyphase e1ectric-power,-.and more-in particular to a polyphase oscillation generating system wherein the frequency of oscillation maybe varied as desired.

An object of this invention is to provide a polyphase oscillator whose frequency -may be varied as desired in a dependable and efiicient manner. A further object'is to provide such a system which is.;adaptable for use, for example, in-a frequency modulation system where the center frequency may-becontrolled for monitoring purposes. A. further-object;is.to provide. a system :Of the. above'characterwh-ich is simple and practical in construction and which is dependable and :adaptablefor use-where it is important toprovide; a desiredgblteciseness of: response to the control influence. Theseiand other objects will be inpart obvious and in part-pointed out below.

Theinventionv accordingly consists in the teaturesiof construct-ion, combinations of elements, arrangements of parts .and i in the several steps and relation-and orderof each of the same to one or more of the others, all as will be illustrativelydescribed-herein, and the scope of the application of which will be. indicated in the following claims.

In the drawings:

Figure 1 is a-simplified circuit diagram showing one embodiment of the invention; and

Figure 2 is similar toF-igure -1, but shows another embodiment ofthe invention.

Under certain circumstances, it is desirable toprovidea polyphase oscillator whose frequency may be variedprecisely as desired in response to some control effect. For example, polyphase oscillation may be utilized advantageously in certain frequency-modulated radio equipment. In such a polyphase oscillating system it is desirable to provide for the precise variation of the frequency of oscillation and to provide an arrangement whereby this frequency may be changed rapidly in response to the varying control influence. In accordance with thepresent invention, a polyphase source of electric power is provided wherein the frequency is'varie'd by electronic means to permit such a rapid response. Illustratively, a-three-phase systemis shown in which inherently the phase angle between the phases is maintainedconstant and the frequency is varied bythesimple procedure of changing a control potential applied to a plurality of electronic devices. This is achieved by changing the impedance of. certain elements of agroup of phase shift circuits whereby the frequency of oscillais inherent-in this. circuit.

Referring particularly to'.Figur.e.1 .of the drawings, a three-,phasecircuitis shown in simplified 'for-m wherein.thefilament andplate supply circuits for the .various tubes. .are omitted, and wherein :a {three-phase radio-lfrequency .power outputis -surnpliedath, B,land-IC. .This circuit.

includes three .threaelement oscillator vacuum tubes 1,..2 V and .3; having cathodes '4, '5 and 56, respectively, grids 1,8 and.l9..and plates [0,. and I2, respectively. The;,.plates-of these tubes are connected to the output leads v.at .A, 'B and C through coupling condensers l3,'l4 andlj5. "The output voltage .of tube. l .is, fedfrom its plate I0 through an.inter,stage coupling condenser 16 to gridctof :tube .2. sSimilarly, theoutput voltages of -:tubes .2 .andu3 are .fed from their plates .resp ively to-the grids}! and .1 ottubes'aand I through interstage coupling condensers l1 and t8. .Ihaplates of tubes I,.Landiareconnecteld to assuitable-source: of high potential .directourrentlthroughmesistors l9,,.2.ll. and .2 I respectively, and the. cathodes ofthesetubes are connectedlto groundv .through resistors 22, 23 and -24, .respectively.

v Grid-8 of tube! is .connectedto ground through a.pair'of series-connectedresistors 25 and.2'6; similarly, grid 9 is connected .to .ground through serieseconnected resistors 21 and 28, ,and .grid 1 ,-..-is :connected .to ground through series-connectedlresistors -2'9 7 and 30. .The juncture .3 I between, resistors .25 and. 26 is connected through .a condenser-.32 to'the juncture-330i .a resistor 34 and the plate! =35of-a three-element control vac-- uum: tube $6. @Control tube=3-6 has a control. grid 31 and ,-a cathode .38. which is connected to ground. In a .-similar-rmanner, .the juncture .39 between resistors :21 and 28. is connected. through a condenser-= to-.the =juncture 4i betweema resistor 42 and the plate 43 of a, control vacuum tube Atwhich has-agridAE and agrounded cathode Afi; ,and, :the juncture :41 between resistors 23 and-'39 is.connected through a condenser-.48 tozthe, juncture 49- between .a resistor 50 andthe plate .il of aqcontrolvacuumtube152 whichhas a grid 53 andaerounded cathode 7-54. .Resistors 34,42 and 50 are..connected to the positive side of ,a. suitable source ofhighpotentialdirect current, the negative.side...of whichis connected to cathodes 38, J46 and .54 through ground. Grids 31, 4.5 and 453 .of the control .tubes 36, .44 g and -52 are connected together andito. one terminal .55 .of a .suitable control potentiaLEm, .the other terminal 56 of which is connected to ground and thence to cathodes 38, 46 and 54.

In this circuit each of the oscillator tubes I, 2 and 3 is connected to provide one of the three phases of the polyphase output and each tube exerts a control influence upon the tube of the next phase so that the three phases are held in their exact 120 relationship. The control effect by each tube upon the tube of the next phase is exerted through an interstage phase shift circuit, there being three such circuits which are identical in components, characteristics and operation. The phase shift circuit by which tube I controls tube 2 is formed by capacitance and resistance connected in series, the capacitance being supplied by a condenser l6 and there being a series resistance circuit to ground formed in part by resistors 25 and 26. The remainder of the resistance circuit is formed by two additional connections to ground which are from juncture 3| through condenser 32, which has low impedance at the high frequency of operation, and thence, through control tube 36 to ground, and through resistor 34 and a connection to ground (not shown) which has low impedance at the high frequency of operation. Thus, it may be considered that grid 8 is connected to ground through resistor 25 to juncture 3| and thence through a network circuit having three parallel branches formed, respectively, by resistor 26, control tube 36 and resistor 34. This is because condenser 32 and the impedance connecting the positive side of resistor 34 to ground may be ignored at the high frequency of operation. I

For purposes of explanation, we will assume that grid 31 of control tube 36 has a normal rid bias and therefore control tube 36 may be considered as an equivalent fixed resistor, the value of which is equal to the internal impedance of the tube, so that in fact resistors 25, 2B and 34 and control tube 36 may be considered as being a single resistor which connects grid 8 to ground and which forms the resistance component of the phase shift circuit. The value of this single resistance component is such with respect to condenser [6 that at the normal frequency of operation there is a 60 phase shift on grid 8 with respect to plate ID. This 60 phase shift between plate In and grid 8 combines with the 180 phase shift produced in the vacuum tube 2 between grid 8 and plate II to produce the net phase shift desired between the two tubes. That is, it will be considered that the 60 phase shift is subtractive with respect to the 180 phase shift of the tube, and thus there is a net phase shift of 120, but if the 60 phase shift is considered as additive with respect to the 180 phase shift of the tube, the net phase shift is 240; and with either the additive or subtractive relationship the desired net effect is obtained.

In a similar manner, oscillator tube 2 controls oscillator tube 3, and oscillator tube 3 controls oscillator tube I. Thus, plate II of tube 2 is connected to grid 9 of tube 3 through an interstage phase shift circuit formed by condenser I1, resistors 21, 28 and 42 and control tube 44; and, plate I2 of oscillator tube 3 is connected to grid 1 of oscillator tube I through an interstage phase shift circuit formed by condenser I8, resistors 23, 30 and 50 and control tube 52. Each of these two phase shift circuits operates the same as the circuit connecting plate I and grid 8, and, during operation, each phase maintains the next phase in its proper relationship, and any tendency for one phase to deviate from this relationship is automatically corrected.

Control tubes 36, 44 and 52 have been considered as having a normal grid bias on their grids so that they act as fixed resistors. However, when there is a control signal at Em, the grid bias of each of these grids is changed with the result that the internal impedance or equivalent resistance of each of the control tubes is changed. Thus, for example, a change in the grid bias of grid 31 changes the equivalent resistance of control tube 36 and thus changes the effective resistance connecting grid 8 of oscillator tube 2 to ground. This tends to cause a change in the phase shift produced by this phase shift circuit because the phase shift depends upon the relative values of the capacitance of condenser I6 and the effective resistance connecting grid 8 to ground. However, as indicated above, the three oscillator tubes I, 2 and 3 control each other, and, therefore, the phase shift relationship between phases does not change, but rather the frequency of oscillation changes in such a manner as to maintain the desired fixed phase shift relationship between phases. In this way the simple action of changing the grid bias of control tubes 36, 46 and 52 changes the frequency of oscillation of the oscillator system. For example, if the control signal Em increases, the impedances of tubes 36, 46 and 52 decrease; then a higher frequency is necessary in order to maintain the phase shift at the oscillator tube grids and the circuit therefore oscillates at this higher frequency. Conversely, a reduction in the control signal Em causes a reduction in the oscillating frequency. The components of the circuit are such as to permit operation within the frequency range desired so that a dependable source of polyphase oscillation is provided. When desired more than three phases may be provided by adding additional oscillator tubes and interstage phase shift coupling circuits, it being understood that due consideration must be given to obtaining trolled in accordance with a control signal Em,

and in addition another control influence may be provided where the frequency of modulation may be additionally regulated. This second control infiuence may be for monitoring purposes so that the normal frequency of oscillation is regulated by a direct current voltage and then the control signal Em exerts a frequency modulating effect to make the system oscillate at frequencies above and below the normal frequency.

In addition to this monitoring control, the embodiment of Figure 2 is provided with means to control automatically the amplitude of oscillation. The amplitude of oscillation is controlled by a set of diode rectifiers in the oscillator tubes. This amplitude control system will now be discussed. Oscillator tubes 51, 58 and 59 correspond to tubes I, 2 and 3, respectively, and in addition to the elements of tubes I, 2 and 3 (which are correspondingly numbered), tubes 51, 58 and 59 are provided with screen grids 30, 6| and 62 which are connected to their respective cathodes, amplitude control grids 63, 64 and 65 and rectifier anodes 66, 61 and 68. Grid 63 of tube 51 is connected to the juncture 69 of a condenser 10 and a resistor 1|; the other side of resistor 1| is): connected te tite positive side on at source oi direct current .potentiaLthe negative'esidei-ofii which is' connected condenser I8 through ground. Juncture .69.,is also connected to the positive side of w-batterwlfi tiie riegative side of which..- is: connected; toeanode 61*. Similarly, grid 64 of tube 58 is connectedeatytheejuncturer 13 to one sideofa groundedcondenser I4, 2. resistor I5 and through a batt'erWI'B -to"anode 58; and, grid'265 of tube 59 is connected at thevjnn'ce turer'll tosa groundedccondenserr18, a.-; ..resistor 'l9rizand through abattery 80,,to.-anode 86; Re sisters 115,-and I9 aresalsoicomieeted to the posi; tive: side: t: a'asource of. direct current totwhich resistor His connected.

Asr..indicated. above, ,thecircuitroi Figurem'szoss, cillatesa in .the. samesgeneraltmanner as doeslathe circuit of Figure-l,..and ,initially., grids 63, 64 and 55 are maintained"positive"so"thatthey do not interfere.. with: theapolyptiasei oscillations Howevenzif:excessive:anrplitudeaofioscillationfishould:2 tend to occur in oneiofithetoscillatorrtubes;suchi asin itube 58; ..the -potentia1.;oficathodea t'wi1-1'xfa1l belowa'that-sofzanodesfiii This will icause current 1' to flow through the diode formerliby cathodi'er and anode 81 so as to lower the potential of grid 63 to such an extent that the amplification of tube 51 is decreased. There is a similar action in each of the other two amplitude control circuits; that is, the diode formed by cathode 6 and anode 68 limits the amplitude of oscillation in tube 58, and the diode formed by cathode 4 and anode 86 of tube 51 controls the amplitude of oscillation in tube 59. Under some circumstances it is desirable to replace batteries 12, I8 and 88 with resistors shunted to ground by a condenser.

The monitoring control referred to above is provided by effecting a change in the basic effective resistances of the three interstage phase shift circuits. Accordingly, resistors 34, 42 and 58 are replaced by three monitor control vacuum tubes BI, 82 and 83. These tubes have, respectively, plates 84, 85 and 86, grids 81, 88 and 89 and cathodes 98, 9| and 92. The plates of these monitor control tubes are connected to the positive side of the direct current source, as were the corresponding resistors in Figure 1, and thence to ground through the direct current sources I81 shunted with capacitors I88 which have low impedance at the high frequency of operation, and cathodes 98, 9| and 92 are connected, respectively, to junctures 33, 4| and 49. Grids 81, 88 and 89 are connected together and to the plate 93 of a vacuum tube 94 which has a cathode 95, a, control grid 96 and grids 91 and 98.

Plate 93 is connected to the juncture 99 between a pair of voltage divider resistors I88 and ml, which are connected in series and form a voltage divider between the positive terminal and the grounded negative terminal of a source of direct current. Grid 99 is connected to the juncture I82 of a condenser I83 (the other side of which is grounded) and a resistor I84 which has its other side connected to the positive side of a source of direct current, the negative side of which is grounded. Control grid 96 is connected to one terminal I85 of a monitor control potential Ec, the other terminal I86 of which is connected to the grounded cathode 95. Illustratively, potential Ec is a direct current potential, and its value controls the current flow through tube 94. This current flow determines the potential of juncture 99 of the voltage divider and, therefore, the grid bias of the grids 81, 88 and 89 of tubes cyclically interconnecting said 20 current connected across sai 815.82 and- 88i Thus: the internaitimpedanceeoti;

tubes lfl 82 and 83 i$ireadilyrcohtroll% I As many possibltembbdinients mayebeimtad' the mechanical featuresiiofstiieaabove invention a and; as the artshereinzdescribedniiightibe: variedt in: various -partsaall without departing .fromithee scope of the inventionait'isiztoirbei un'derstood:thati alt n iatte'r hereinabove -se forth; on showrriirttlie accompanyingdrawing oebe interpreted? as: illustrative andinot limitin'gisenset l.- A' polyphase oscillation generating system'r com-prising ai plurality of amplifier"stags;-.afiplu rality of I non-resonant phas shifting: networkss tag's and com posedor reactive andi-resistive inipedanc means the resistive ini'p'edante means or eachof sai networks-melodic a ria-ii of 'electronic -discharges devices conrrecte'd a source' o'fspas devices;- m 'ea-n's for 'varyi g thei internal imped ance' of one of 'said electronic discliargedevio of each pair; and differentzmeans ror -varymg s internal impedanceof th'e other of said electronic-r discharge "devices "of eaclip'ai herby tliie opera ating-frequencyof the systeinniay be al-teredt- 2. A system as claimed in claim 1 wherein each of said amplifier stages is represented by a vacuum tube having a cathode, a plate and a plurality of grids, further comprising means for limiting the amplitude of oscillations generated by the system, said last means including a diode anode placed in each of said tubes adjacent the cathode thereof, an impedance connected to each cathode whereby the cathode potential will vary with the current through the tube, means for biasing said diode anode to a potential more negative than that of the associated cathode except upon occurrence of amplitudes above a predetermined limit, a condenser shunting said diode anode, said cathode and said impedance, and means connecting said diode anode to one of the grids of one of said tubes.

3. A system as claimed in claim 2, wherein the diode anode of each stage is connected to a grid of the preceding stage.

4. A system as claimed in claim 3, wherein each stage comprises a pentode tube and wherein the diode anode of each stage is connected to the screen grid of the preceding stage.

5. A polyphase oscillation generating system comprising a plurality of amplifier stages, a plurality of non-resonant phase shifting networks cyclically interconnecting said stages and composed of capacitive and resistive impedance means, the resistive impedance means of each of said networks including a pair of triodes, means connecting the plate of one triode of each pair to the cathode of the other triode, a condenser forming part of said capacitive impedance means connected to said plate and said cathode, a source of space current connected across said two triodes in series, means for grounding the cathode of said one triode at least for the frequencies in the operating range of the system, means for applying a signal potential to the grid of said one triode whereby the operating frequency of the system may be modulated, and means for applying a control potential to the grid of said other triode whereby the mean operating frequency of the system may be varied.

6. A system as claimed in claim 5, wherein the plate of said other triode is grounded for the frequencies in the operating rang of the system.

7. A system as claimed iii-claim 6, wherein the means for applying said control potential comprise a voltage divider, a connection between an intermediate point of said voltage divider and the grid of saidother triode, an electronic discharge device shunting part of said voltage divider, and means for varying the conductivity of said electronic discharge device.

8. A system as claimed in claim 7, wherein said electronic discharge device is a pentode.

9. A system as claimed in claim 5 wherein each of said amplifier stages is represented by a vacuum tube havin a cathode, a control grid, a screen grid and a plate, the plate of each stage being coupled to the control grid of a succeeding stage over a respective one, of said phase shifting 15 networks, further comprising means for limiting the amplitude of oscillations generated by the system, said last means including a diode anode placed in each of said tubes adjacent th oathode thereof, a resistor connected between each cathode and ground, means for biasing said diode anode to a potential more negative than that of the associated cathode except upon occurrence of amplitudes above a predetermined limit, a condenser shunting said diode anode, cathode and cathode resistor, and means connecting the diode anode of each stage to the screen grid of the preceding stage.

GEORGE T. ROYDEN. REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 19 Number Name Date 1,745,559 Schrack et a1 Feb. 4, 1930 1,972,535 Page Sept. 4 1934 2,024,489 Van Derpol et a1. Dec. 17, 1934 2,055,090 Rust Sept. 22, 1936 2,236,985 Bartelink Apr. 1 1941 2,321,269 Artzt June 8, 1943 2,373,437 Van Derlyn et al. Apr. 10, 1945 OTHER REFERENCES 25 et al. 2503613.2. 

